Embryology Problem Based Questions (Langman - Q5)

ANATOMY AIIMS, GROSS ANATOMY, EMBRYOLOGY, NEUROANATOMY, MICROANATOMY, APPLIED/ CLINICAL ANATOMY

What is mosaicism, and how does it occur?

Answer:

Mosaicism is a genetic condition that arises when an individual has two or more populations of cells with different genetic compositions within their body. In other words, some of the individual's cells have one set of genetic information, while others have a different set.

Mosaicism occurs due to genetic mutations that occur during early stages of embryonic development. During this time, the fertilized egg divides repeatedly to form a group of cells that will eventually develop into an entire organism. If a mutation occurs during one of these early cell divisions, then the resulting organism will have a mixture of cells with the mutation and cells without the mutation.

Mosaicism can occur in any type of cell, including those that give rise to tissues and organs, which can lead to a wide range of physical and developmental abnormalities depending on the type of mutation involved and which tissues are affected. Some examples of conditions caused by mosaicism include certain types of cancer, skin disorders, and developmental disorders such as Down syndrome.

Here are some examples of mosaicism:

Down Syndrome Mosaicism: Down syndrome is typically caused by an extra copy of chromosome 21, but in some cases, individuals have a mixture of cells with the extra chromosome and cells without it. This is known as mosaic Down syndrome. Mosaic Down syndrome can result in a milder phenotype and fewer health problems than the typical form of Down syndrome.

Reference:

Hook, E. B. (1981). Mosaicism for trisomy 21: a review. Human Genetics, 58(1), 1-12.

Segmental Neurofibromatosis Type 1 Mosaicism: Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder characterized by the growth of benign tumors along nerves throughout the body. Segmental NF1 mosaicism is a rare form of the disorder in which only certain parts of the body are affected due to mosaicism.

Reference:

Kluwe, L., Friedrich, R. E., & Mautner, V. F. (2011). Segmental neurofibromatosis type 1: a rare manifestation with a possible risk of malignancy. Acta Dermato-Venereologica, 91(6), 686-687.

Pigmentary Mosaicism: Pigmentary mosaicism refers to a group of disorders in which there is a mosaic distribution of skin pigmentation. One example is hypomelanosis of Ito, which is characterized by a distinctive pattern of hypopigmentation along the lines of Blaschko.

Reference:

Happle, R. (2010). Mosaicism in human skin: understanding the patterns and mechanisms. Archives of Dermatology, 146(7), 859-876.

Mosaic Turner Syndrome: Turner syndrome is a genetic disorder that affects females and is caused by the absence of all or part of one X chromosome. In some cases, females with Turner syndrome have a mosaic pattern of cells with the missing X chromosome and cells with two X chromosomes.

Reference:

Sybert, V. P. (2016). Turner syndrome. New England Journal of Medicine, 376(8), 743-752